This invention relates to an optical coupling apparatus including a semiconductor light emitting device and an optical fiber that are optically connected to each other. More particularly, the invention relates to a single lens optical coupling apparatus that attains optical coupling by use of a single lens.
A known optical coupling apparatus allows an outgoing beam from a semiconductor laser to be incident into an end face of an optical fiber through a lens, and optical coupling is attained between the semiconductor laser and the optical fiber through the single lens, as described in JP-A-05-150146. This reference discloses a construction in which the semiconductor laser, the lens and a light reception device are mounted onto a substrate having thick portions on both sides thereof that are parallel to an optical axis to suppress the change of optical coupling in the optical axis direction and to reduce an optical axis error.
Another reference, JP-A-11-330564, describes optical coupling between an optical semiconductor device and an optical fiber by use of a single lens. The optical semiconductor device and the lens are mounted onto a block. The block is arranged on a heat sink and is encompassed by a package. An optical fiber is inserted and fixed into a cylindrical optical fiber fixing portion disposed on a side surface of the package. Fixing members capable of deformation are interconnected to a package main body to prevent an optical axis error of the package resulting from thermal expansion of the heat sink when the heat sink is screw-fixed to mount an optical communication appliance. Still another reference, JP-A-2001-284699, discloses a construction in which two lenses are used to optically couple a semiconductor laser and an optical fiber, and the semiconductor laser and a first lens are mounted onto a base and are disposed on a bottom plate of a package through a Peltier device. A fitting cylinder is so fitted as to protrude from inside and outside of the package, and a second lens and the optical fiber are disposed inside the cylinder and at an end portion, respectively.
The inventors of this invention have found that the constructions of the known references are not yet satisfactory as a construction of a single lens optical coupling apparatus that is very susceptible to influences of thermal deformation of a base and surrounding portions when service life of the apparatus is extended or when the apparatus is applied to long-distance optical transmission.
Evaluation items of performance of an optical coupling apparatus include optical coupling temperature characteristics (hereinafter called xe2x80x9ctracking errorxe2x80x9d) relating to stability of optical coupling in a temperature range from a low temperature to a high temperature. The tracking error occurs mainly as an operating temperature of the optical coupling apparatus changes to invite thermal deformation, and this thermal deformation in turn invites a change of the optical coupling state between a semiconductor light emitting device and an optical fiber.
JP-A-2001-284699 as the known reference described above employs a confocal optical system that uses two lenses and suppresses the change of optical coupling due to thermal deformation. The confocal optical system has a feature in that tolerance of a positioning error on the change of optical coupling becomes greater between the two lenses. The optical coupling apparatus makes the most of this feature, exhibits a small change of optical coupling even when thermal deformation develops, and makes it easier to satisfy the tracking error specification. However, the confocal optical system using the two lenses increases the number of components and the number of assembly steps and is likely to invite the increase of the production cost.
It is more advantageous to establish optical coupling by using one lens in order to reduce the number of components as well as the number of assembly steps and to lower the production cost. However, because the optical coupling system using one lens does not have a broad tolerance portion of the positioning error of the confocal optical system, the change of optical coupling unavoidably occurs due to very limited thermal deformation. Therefore, the optical coupling apparatus of the one-lens optical system must employ a component construction that makes the difference of the thermal expansion ratios smaller than that of the component construction of the confocal optical system to suppress thermal deformation. Because the optical coupling apparatus is constituted by a plurality of materials having mutually different thermal expansion ratios, however, it is extremely difficult to completely eliminate thermal deformation unless specific materials are used to form the components. When such specific components are employed, the production cost increases with the result that the effect of lowering the cost of production by using one lens is lost.
It has been found that the form of JP-A-05-150146 and JP-A-11-330564 occupies a large ratio to the length of a so-called xe2x80x9cbase portionxe2x80x9d of the housing, and is greatly susceptible to deformation of the base. Therefore, it is believed difficult to sufficiently reduce the tracking error. In addition, because JP-A-11-330564 does not mount the Peltier device, temperature control by the Peltier device is not possible. When any temperature change occurs, thermal expansion and thermal deformation of the block further increase the positioning error between the semiconductor light emitting device and the lens in the direction of height. Consequently, the position of the laser beam to be condensed to the optical fiber greatly changes, and the tracking error specification cannot be satisfied easily.
It is therefore an object of the invention to provide an optical coupling apparatus that can solve the problems described above.
To accomplish this object, the invention employs a construction that can insure long service life and can be applied to long distance optical communication even in a form susceptible to influences of thermal deformation of a base and surrounding components such as in the case of a single lens optical coupling apparatus.
For example, a construction capable of satisfying an optical coupling change of xc2x10.5 dB within a temperature range from xe2x88x9220xc2x0 C. to 75xc2x0 C. as a tracking error specification can be accomplished at a low cost of production.
The invention can specifically take the following forms, for example.
(1) An optical coupling apparatus including a base; a temperature controlling device disposed on the base; a substrate arranged on the temperature controlling device and having mounted thereto a semiconductor light emitting device and a lens into which rays of light from the semiconductor light emitting device are introduced while being diffused; a through-hole portion formed in a housing wall portion installed on the base, penetrating through the housing wall portion and having a wall surface portion longer than a thickness of the housing wall portion; and an optical fiber communicated with the through-hole portion and receiving converged light from the lens introduced thereto; wherein a length of the substrate in a direction connecting the light emitting device to the optical fiber is within a range from 0.1 to 0.25 with respect to a length of the base sandwiched by the housing walls of the substrate.
(2) The optical coupling apparatus described in the construction (1) further comprises an optical isolator which communicates with the through-hole portion and into which converged light is introduced on the side of the lens from an end portion of the optical fiber, wherein the optical isolator and at least a part of the optical fiber are arranged inside a region of the through-hole portion encompassed by the housing walls, and the end portion of the optical fiber is arranged at a position within three times the thickness of the housing wall from an outer or inner side surface of the housing wall in a direction connecting the light emitting device and the optical fiber. Alternatively, the end portion of the optical fiber is arranged within a range of 3.0 mm from the outer or inner side surface of the housing wall.
(3) In the optical coupling apparatus described in the construction (1) or (2), the end portion of the optical fiber is formed at a position within a range from 3.5 to 12.5 times the thickness of the lens from the light emitting device. Alternatively, the end portion of the optical fiber is arranged at a position within a range from 3.5 to 7.5 mm from the light emitting device.
(4) In the construction of the optical coupling apparatus described in any of (1) to (3), the temperature controlling device is arranged within a range of 6.0 mm from the inner side wall of the housing wall in a direction of the temperature controlling device connecting the light emitting device to the optical fiber.
(5) An optical coupling apparatus including a terminal substrate having a wiring layer and lead terminals connected to the wiring layer that are applied to the housing wall, wherein a temperature controlling device is electrically connected to the terminal substrate through wires, and this connection portion is positioned closer to the optical fiber than the lead terminals corresponding to the temperature controlling device.
(6) An optical coupling apparatus wherein a terminal substrate having a wiring layer and lead terminals connected to the wiring layer are provided to the housing wall, a thermistor is mounted to the substrate and is electrically connected to the wiring layer of the terminal substrate through wires, the temperature controlling device is electrically connected to the wiring layer of the terminal substrate through wires and a length of the wiring layer on the terminal substrate corresponding to the thermistor is smaller than a length of the wiring layer on the terminal substrate corresponding to the temperature controlling device.
(7) In the optical coupling apparatus, a terminal substrate having a wiring layer and lead terminals connected to the wiring layer are provided to the housing wall, the wiring layer includes a relay substrate having a wiring layer electrically connected to the wiring layer through wires, and is electrically connected to the substrate for mounting the light emitting device, through the wiring layer of the relay substrate and through wires, and the light emitting device is arranged closer to the optical fiber than the lead terminals corresponding to the light emitting device.
Even when thermal deformation and warp deformation occur with the change of an ambient temperature and due to a thermal load, the constructions of the optical coupling apparatuses described above can suppress the change of optical coupling between the semiconductor light emitting device and the optical fiber, and can also satisfy the specification of the tracking error even when thermal deformation and warp deformation occur. In other words, even when warp deformation of the base occurs with the temperature change, fluctuation of the laser beam outgoing from the lens mounted to the substrate in its traveling direction can be suppressed when the length of the substrate having the temperature controlling device mounted thereto is kept within a range from 0.1 to 0.25 to the length of the base. The housing wall undergoes deformation in such a fashion as to fall down towards the inside of the housing with the connection position with the base as a support point. Therefore, when a part of the optical isolator or the distal end of the optical fiber is arranged within a predetermined range of the through-hole portion encompassed by the housing wall portions, the positioning error of the distal end of the optical fiber can be reduced. Furthermore, because the housing walls so operate as to suppress thermal deformation of the base, thermal deformation becomes smaller at positions closer to the housing walls. For this reason, when the temperature controlling device having the semiconductor light emitting device and the lens mounted thereto is arranged within a predetermined range close to the housing wall portions, deformation of the substrate to which the temperature controlling device is mounted can be reduced, and the positioning error of the laser beam outgoing from the lens resulting from this deformation can be suppressed. Because the invention employs the construction and the component arrangement for suppressing the positioning error of the distal end of the optical fiber and the positioning error of the outgoing beam from the lens, the invention can suppress the change of optical coupling resulting from thermal deformation to a low level without using a specific component construction. In this way, the invention can satisfy the tracking error specification even in an optical coupling apparatus of a one-lens optical system.
Because the optical isolator and the optical fiber are put into the housing wall portions, the protrusion distance of the optical fiber protruding outside from the housing wall portion can be reduced. In consequence, the overall size and shape of the optical coupling apparatus can be reduced and high-density packaging to the packaging substrate can be achieved.
The temperature controlling device is electrically connected to the terminal substrate provided to the housing, and this connection portion is arranged at a position closer to the optical fiber side than the lead terminal corresponding to the temperature controlling device. Therefore, a wide space can be secured on the opposite side to the optical fiber while interposing the temperature controlling device. An expansion unit for improving functions can be easily arranged in this space and the functions of the optical coupling apparatus can be improved without inviting a drastic change of the construction. The length of the wire connecting the terminal substrate to the temperature controlling device can be formed to the minimum length and calorific power due to the increase of an impressed current can be reduced. Therefore, even when any change occurs in the ambient temperature, defect of the wires can be prevented, and the temperature controlling device can be stably driven to provide an optical coupling apparatus having high reliability. Furthermore, because the invention employs the single lens for optically coupling the semiconductor light emitting device and the optical fiber, the invention can reduce the number of components and can accomplish easy assembly.
The invention can provide the optical coupling apparatus of the one-lens optical lens system that can stably keep optical coupling between the laser diode and the optical fiber and can satisfy the tracking error specification.
Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings.